1. Field of the Invention
The present invention relates in general to trip shank assemblies for mounting the shank of an earthworking tool, such as a plow or other cultivating implement, to the tool bar of a soil tilling implement, and more specifically relates to such assemblies which trip upon encountering an immovable obstruction and then automatically reset in their operative position after having passed the obstruction.
Cultivatable land often has at least some hidden obstructions in the soil in the form of large and usually immovable objects such as stumps, rocks, or roots which objects may cause considerable damage to earthworking tools which are used in tilling the soil.
Prior art devices have attempted to eliminate, or at least minimize, the damage to earthworking tools by providing trip shank assemblies that allow the earthworking tool to pivot upwardly and rearwardly when encountering an obstruction.
For example, U.S. Pat. Nos. 4,293,043; 4,068,723; 4,054,177; and 3,949,814 provide trip shank mechanisms that utilize a spring biased toggle link assembly. These prior art devices maintain the earthworking tool in the ground under normal conditions but allow the earthworking tool to pivot upwardly and rearwardly when it encounters an obstruction. The toggle link assembly of these prior art devices include angularly related link portions that are pivotally connected and have biasing means exerting a constant compressive force thereon. These prior art devices utilize an "off-center" pivotal connection by angularly connecting the link members together. Stop means are provided to maintain the "off-center" arrangement by preventing the biasing means from forcing the angularly related link members into linear alignment. This arrangement, however, requires biasing means having a high compressive force to maintain the earthworking tool in a working position under normal working loads. This is due to the fact that the toggle link mechanism is already in a partially tripped position due to the angular relationship of the link members. Because the compressive force is high and also because the force is constant or increases throughout the operation of the toggle link mechanism, when the earthworking tool encounters an obstruction the tool is exposed to the obstruction for a relatively long period of time. These devices therefore only slightly minimize the damage to the earthworking tool. In addition, these devices have a significant number of parts requiring a substantial initial cost as well as significant repair costs.
U.S. Pat. No. 4,312,408 discloses an assembly wherein the force of the biasing means progressively decreases as the earthworking tool pivots upwardly and rearwardly. However, this device is incapable of returning the tool into the soil to the operating position and the operator must manually provide for a return movement of the earthworking tool to its operating position.
The present invention overcomes these prior art inadequacies by providing a toggle link mechanism having substantially linearly aligned link members having a pivotal connection connecting the link members together which connection is "off-center" when the earthworking tool is in a working position. This allows the toggle link mechanism to play a larger part in maintaining the earthworking tool in a working position as opposed to the prior art devices wherein the biasing means provides the major force for maintaining the earthworking tool in a working position. Therefore, biasing means having less of a compressive force can be utilized in the present invention to maintain the earthworking tool in a working position. In addition, the present invention provides an arrangement of biasing means and toggle link mechanism wherein the compressive force decreases as the toggle link mechanism collapses. The present invention therefore allows the earthworking tool to pivot away from an obstruction in the ground with little resistance thereby decreasing the time the tool is exposed to the obstruction. The toggle link mechanism also provides sufficient force to return the earthworking tool to its operating position. Furthermore, the toggle link mechanism is of relatively simple design having a minimum number of parts thereby reducing the initial cost of such device as well as the cost of repair.
It is a principal object of the present invention to provide an improved trip shank mechanism which will maintain an earthworking tool in working position under normal conditions and allow the earthworking tool to pivot upwardly and rearwardly when encountering an obstruction.
A further object of the present invention is to eliminate or substantially reduce the amount of damage incurred when an earthworking tool encounters an obstruction.
Another object of the present invention is to provide a trip shank mechanism having a minimum number of parts and being of a relatively simple design.
Still another object of the present invention is to provide a trip shank mechanism that requires a relatively low compressive force to maintain the earthworking tool in a working position.
Still another object of the present invention is to provide a trip shank mechanism wherein the mechanical advantage of the biasing means decreases as the toggle linkage collapses.
A further object of the present invention is to provide a trip shank mechanism wherein the earthworking tool is returned to a working position after moving over an obstruction.